Due to low ignition energy and wide range of flammability limit, explosion hazard of hydrogen/ammonia fuel must be evaluated to ensure safety application. In this work, effects of equivalence ratio, ammonia addition and initial pressure on the flame morphology and explosion pressure are revealed. The results demonstrate that effects of three factors on explosion hazard are ranked from the most important to the least important as initial pressure, equivalence ratio and ammonia hydrogen. The cellular flame formation by varying the equivalence ratio could be mainly attributed to the diffusional-thermal instability. The expanding flame of Phi = 0.8, 1.0 and 1.5 tends to be stable with ammonia addition. As initial pressure increases, there exists a joint and competitive effect of the diffusionai-thermal instability and hydrodynamic instability. Maximum explosion pressure of Phi = 0.8, 1.0 and 1.5 decreases monotonously with ammonia addition and increases linearly with initial pressure. The explosion pressure prediction is underestimated using the smooth flame model and reproduced satisfactorily using the wrinkled flame model. By varying equivalence ratio, ammonia addition and initial pressure, the most elementary reaction that enhances laminar flame velocity is R9 and the first two inhibiting reactions to laminar burning velocity are R10 and R168. (C) 2018 Elsevier Ltd. All rights reserved.